hi, you're right to be suspicious - this is a scam tactic that is trying to trick you into installing malware, so don't download or execute this kind of stuff just because of a popup or redirect on a website! updates are handled automatically by firefox so you don't have to download anything for that (and you can always initiate a manual check for updates in the firefox menu ≡ > help ? > about firefox).

we suspect this is coming form "malvertising" (=ads placed on legitimate websites that redirect you to this fraudulent message), so using an adblocking addon like https://addons.mozilla.org/firefox/addon/ublock-origin/ would also help with that.

I found a fake Firefox update

Firefox updates have been done internally in Firefox since Firefox 1.5 almost eleven years ago.

Also does it really make sense for Mozilla to host a Firefox download or update at a random weird name site each day outside of a *.mozilla.org url?.

You can see how random the sites are in the list at https://support.mozilla.org/en-US/forums/contributors/712056